Screened massive expansion of Schwinger-Dyson equations

A general formal derivation of the screened massive expansion is provided by Schwinger-Dyson equations. Some known issues of the expansion are clarified and a more general framework is established for a natural extension of the method to two loop or to amplitudes that are not directly defined by a generating functional. For instance, a one-loop screened expansion is given for the effective gauge-parameter-independent gluon propagator that arises from the pinch technique.